1. Field of the Invention
The present invention relates to crystalline oxotitanylphthalocyanine having a particular crystal form and an electrophotographic photoreceptor using a composition containing the crystalline oxotitanylphthalocyanine in a charge generating layer.
2. Description of Related Art
Electrophotographic photoreceptors (hereinafter sometimes simply referred to as "photoreceptor") currently subjected into practical use are classified into an inorganic photoreceptor using an inorganic photoconductive material excellent in sensitivity and durability, and an organic photoreceptor using an organic photoconductive material. The inorganic photoconductive material include a ZnO (zinc oxide) series material, a CdS (cadmium sulfide) series material, an Se series material, such as a--Se (amorphous selenium) and a--AsSe (amorphous arsenic selenide), and a--Si (amorphous silicon) series material.
However, the ZnO series material cannot stably form an image for a long period of time because the charging property of a sensitizing material added is deteriorated due to corona discharge, and photobrowning occurs due to exposure. Furthermore, a photoreceptor equipped with a photosensitive layer formed by dispersing ZnO in a binder resin is of low sensitivity and low durability. The CdS series material cannot provide stable sensitivity under a high-humidity environment, and the Se series material has a strong toxicity, and its crystallization easily proceeds by an external factor, such as temperature and humidity, to lower the charging property or to form whitedotson an image. A photoreceptor equipped with a photosensitive layer using the CdS series material and the Se series material is low in heat resistance and storage stability, and since it has a toxicity, a problem is involved in its disposal and environmental pollution may be caused. Although the a--Si series material, which is receiving attention as a pollution free material, has high sensitivity and durability, since the photosensitive layer is formed by a plasma CVD (chemical vapor deposition) method, image defects are formed and its productivity is low due to the production process, so as to increase the production cost.
On the other hand, the organic photoconductive material is generally easy in formation of a thin film by coating, and has a low production cost and high mass-productivity. Because the organic material itself includes various kinds, a photosensitive layer having a high storage stability and a low toxicity can be produced by appropriate selection thereof, and it can be easily disposed. Furthermore, the setting of the wavelength range of light absorption can be easily changed, and the electrophotographic characteristics can be easily controlled by the combination of the materials. Therefore, in recent years, improvement in sensitivity and durability has been extensively studied, and the organic materials are frequently employed. A photoreceptor includes a function separated type, in which a photosensitive layer having a laminated structure comprising a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance is formed on a conductive support, and a single-layer type, in which a photosensitive layer containing a charge generating substance and a charge transporting substance is formed on a conductive support. In the photoreceptor using the organic material, the function separated type is mainly subjected to studies and developments.
As the charge transporting substance, many substances having various molecular structures are developed, and for example, Japanese Unexamined Patent Publication JP-A-54-59143 discloses a hydrazone series charge transporting substance, Japanese Unexamined Patent Publication JP-A-58-198043 discloses a stilbene and styryl series charge transporting substance, and Japanese Examined Patent Publication JP-B2-58-32373 discloses a triarylamine series charge transfer substance. In addition, a phenothiazine series compound, a triazole series compound, a quinoxaline series compound, an oxadiazole series compound, an oxazole series compound, a pyrazoline series compound, a triphenylmethane series compound, a dihydronicotinamide series compound, an indoline series compound and a semicarbazone series compound are developed.
In recent years, an image forming apparatus is widely spread, such as a laser printer, in which a laser light source is used instead of a white light source to realize a high speed printing, a high quality image and a non-impact operation. In particular, various modes using a semiconductor laser, which has been extensively developed in recent years, as a light source are attempted, and a photoreceptor having high sensitivity to a long wavelength region of about 800 nm, which is a wavelength range of laser light, is highly demanded.
An organic material that satisfies the demand includes, for example, a squalic acid methine series dye, an indoline series dye, a cyanine series dye, a pyrylium series dye, a polyazo series dye, a phthalocyanine series dye and a naphthoquinone series dye. However, the squalic acid methine series dye, the indoline series dye and the cyanine series dye are poor in stability, particularly characteristics for repeated use, although they can be sensitive to the long wavelength region, and the polyazo series dye is difficult to make sensitive to the long wavelength region, and is poor in productivity. The naphthoquinone series dye is poor in sensitivity.
On the other hand, the phthalocyanine dye has a high sensitivity to light of the long wavelength region and excellent in stability in comparison with the other dyes. It is disclosed in Manabu Sawada, Dyes and Chemicals, Vol. 24, No. 6, pp. 122-128, (1979) that phthalocyanine series compounds are different in sensitivity peaks and physical properties depending on the presence and absence and the kind of the central metal, and further the physical properties are changed depending on the crystal form thereof. Furthermore, it is apparent from U.S. Pat. No. 3,357,989, Japanese Unexamined Patent Publication JP-A-49-11136, U.S. Pat. No. 4,214,907 and British Patent 1,268,422 that while the sensitivity peak of a photoreceptor using a metallic phthalocyanine compound changes depending on the central metal, it is in the side of a relatively long wavelength of from 700 to 750 nm. Therefore, it is important to study and develop a photoreceptor with taking the crystal form of phthalocyanine into consideration.
Techniques of an electrophotographic photoreceptor, in which a phthalocyanine compound having a particular crystal form is selected, have been reported. For example, Japanese Unexamined Patent Publication JP-A-60-86551 discloses an example using a metal-free phthalocyanine, Japanese Unexamined Patent Publication JP-A-62-133462 discloses an example using phthalocyanine containing aluminum, and Japanese Unexamined Patent Publication JP-A-59-49544 discloses an example using phthalocyanine containing titanium as the central metal. Japanese Examined Patent Publication JP-B2-5-55860 discloses a photoreceptor comprising a charge generating layer containing a titanium phthalocyanine compound and a binder resin having accumulated thereon a charge transporting layer containing a hydrozone series compound and a binder resin. Furthermore, Japanese Unexamined Patent Publication JP-A-10-142819 discloses a photoreceptor containing a phthalocyanine series compound as a charge generating substance and a specific styryl compound as a charge transporting substance. As the central metal of a phthalocyanine compound, various metals, such as indium and gallium, have been known.
Among the phthalocyanine compounds, oxotitanylphthalocyanine has a high sensitivity, and it has been disclosed that it is classified into many crystal forms depending on a diffraction angle of an X-ray diffraction spectrum in Electrophotography (The Society Journal, Society of Electrophotography of Japan), Vol. 32, No. 3, pp. 282-289. As the crystal form of oxotitanylphthalocyanine, Japanese Unexamined Patent Publications JP-A-61-217050 and JP-A-61-239248 disclose a type, Japanese Unexamined Patent Publication JP-A-62-67094 discloses A type, Japanese Unexamined Patent Publications JP-A-63-366 and JP-A-63-198067 disclose C type, Japanese Unexamined Patent Publications JP-A-63-20365, JP-A-2-8256, JP-A-1-17066 and JP-A-7-271073 disclose Y type, Japanese Unexamined Patent Publication JP-A-3-54265 discloses M type, Japanese Unexamined Patent Publication JP-A-3-54264 discloses M-.alpha. type, Japanese Unexamined Patent Publication JP-A-3-128973 discloses I type, and Japanese Unexamined Patent Publication JP-A-62-6 7094 discloses I and II types.
The crystal forms of oxotitanylphthalocyanine, the lattice constant of which is known from structural analysis, are C type, Phase I type and Phase II type. Phase II type belongs to a triclinic system, and Phase I type and C type belong to a monoclinic system. When the crystal forms described in the publications are analyzed from these known crystal lattice constants, A type and I type belong to Phase I type, .alpha. type and B type belong to Phase II type, and M type belongs to C type. These explanations are found in, for example, Journal of Imaging Science and Technology, Vol. 37, No. 6, p. 607 to 609 (1993).
Japanese Unexamined Patent Publication JP-A-59-49544 specifically discloses a photoreceptor comprising a support having formed thereon a charge generating layer by vapor deposition of oxotitanylphthalocyanine, and further formed thereon a charge transporting layer containing 2,6-dimethoxy-9,10-dihydroxyanthracene as a main component. However, the photoreceptor is of a high residual potential to make restrictions on the usage thereof, and is poor in reproducibility of electric characteristics due to unevenness in film thickness obtained by a vapor deposition method. Furthermore, the photoreceptor is low in mass productivity in an industrial scale. Japanese Unexamined Patent Publication JP-A-61-109056 discloses a photoreceptor comprising a charge generating layer containing an oxotitanylphthalocyanine compound and a binder resin having accumulated thereon a charge transporting layer containing a hydrozone compound and a binder resin. While the photoreceptor disclosed in the publication has a sensitivity in a wavelength region of about 800 nm, it does not satisfy a high quality image and a high speed operation that are demanded in practical use. As described in the foregoing, oxotitanylphthalocyanine is low in sensitivity and is poor in potential stability on repeated use.
In an electrophotographic photoreceptor, it is general that a charge transporting substance that is effective to a particular charge generating substance is not necessarily effective to the other charge generating substance, and a charge generating substance that is effective to a particular charge transporting substance is not necessarily effective to the other charge transporting substance. In other words, it is necessary that a charge generating substance and a charge transporting substance are suitably combined to use in a photoreceptor, and when the combination is not suitable, not only the sensitivity is decreased, but also the residual potential becomes high, and the charge is accumulated by repeated use to adhere a toner on a non-image area. As a result, a clear image cannot be obtained due to fogging in the background. While the combination of a charge generating substance and a charge transporting substance is important, there is no general rule to select the combination, and it is difficult to find out a charge transporting substance that is suitable to a specific charge generating substance.
As described in the foregoing, there has been no photoreceptor using a phthalocyanine series compound, which is an organic photoconductive material having a sensitivity in a long wavelength range, particularly oxotitanylphthalocyanine having a high sensitivity, that satisfies practical demands in photosensitivity characteristics, characteristics on repeated use, and stability.